Protection of aluminum



Patented May 13, 1941 assignments, to Wingfoot Corporation, Akron, Ohio,a corporation of Delaware No' Drawing. Application .iune' i, 1938,Serial No. 211,947

6 Claims.

This invention relates to the treatment of gasoline tanks and, moreparticularly, to the protection of such tanks, especially gasoline tanksof aluminum or aluminum containing alloys, from corrosion resulting fromthe action of metal derivatives in the gasoline.

Corrosion is, of course, a widespread phenomenon whose seriousconsequences in some industrial applications have prompted much study ofthe problem. The causes of corrosion and the methods of preventing orretarding it varywidely according to the materials and conditions ineach case.

During comparatively recent years, aluminum has become a constructionmaterial of increasing application, one of its outstandingcharacteristics from a practical standpoint being its resistance tocorrosion under many conditions which other materials do not readilywithstand. Aluminum and aluminum alloys have found especially wideapplication in the construction of aircraft of both the heavier-than-airand the lighter-than-air types because of the desirability of minimizingweight in these structures. Some rather peculiar corrosion difiiculties'arise when aluminum and aluminum-containing alloys are used for gasolinetanks, as in aircraft. Water-free gasoline appears to have no corrosiveeffect on an aluminum or aluminum alloy tank, and this is also true ofgasolines which contain metallic compounds added to give anti-knock orother desiraable properties to the gasoline. However, gasoline whichcontains a compound of a metal which is electropositive to aluminum willattack an aluminum or aluminum alloy tank if the gasoline containswater. Since aluminum and aluminum containing alloys are being used moreand more in the construction of transportation vehicles, such as ships,railroad cars, etc., and particularly heavierand lighter-than-air craft,the prevention of corrosion in aluminum or aluminum alloy gasoline tanksassumes constantly increasing importance and this is particularly truebecause of the wider use in gasoline of metal derivatives such astetraethyl lead, tin tetra ethyl, etc. as anti-knock compounds.

Although these metal compounds are relatively insoluble in water andalthough it is not readily to be expected that they will undergo anysubstantial amount of ionization under the conditions involved, it hasbeen found that, when the metals of these compounds are electropositiveto aluminum, they are often reduced to the metallic state byelectrolytic action, an equivalent amount of aluminum going intosolution. Moreover, the

dissolving out of the aluminum from the gas tank structure may be solocalized as to; promote the separation of metallic crystals ofaluminum, thereby increasing the" amount of corrosion. Furthermore, suchelectrolytic action apparently accelerates the ordinary corrosion of thealumi-- num as by the action of varioussalts in the solution, etc;Although various methods have been suggested for reducing or retardingthe amount of corrosion of aluminum under given circumstances, thesemethods" are more or less peculiar to the conditions of each particularvcase. Therefore, the corrosion of aluminum gasoline tanks in thepresence of water and gasoline which contains compounds of metalselectropositive to aluminum, presents itsown special difficulties andnecessitates individual treatment.

Since, as previously indicated, such corrosion ordinarily takes placeonly in the presence of water, one method of avoiding the diflicultyconsists in removing water from or preventing its entrance into thegasoline tank as by the use of suitable absorbent materials. Thisprocedure, however, offers certain mechanical difliculties andnecessitates constant control to ascertain when-the absorbent materialis spent and must be replaced. Moreover, it is rather difficult toentirely prevent water from getting into the gasoline system in manyinstances. This water may be introduced in a number of ways. Forexample, in lighter-than-air craft, it is sometimes necessary to pumpthe gasoline from one storage tank to another to maintain the balance ofthe ship while it is in flight. For instance, in a ship equipped withmotors located at difierent positions along the length of the ship, as,for example, in a ship equipped with two motors near the front and twomotors near the stern, if all of the motors are operating at the startof a voyage and during the course of the voyage it becomes necessary ordesirable to discontinue the operation of the two motors toward thefront or the two motors toward the stern, it is necessary to pumpgasoline from tanks in one position of the ship to tanks in anotherposition in order to maintain the desired balance. Such transfer ofgasoline is not uncommon during Zeppelin flights and where it istransferred several times during a flight, it may take up considerablewater.

It has now been found that the difliculties of attempting to remove orprevent the entrance of water by mechanical devices and absorbents maybe avoided and the corrosion of the tank may be prevented by adding a.water-soluble chromate such as sodium or potassium dichromate or so:gasoline tank or to the water. 7 case, it will be dissolved by theWater when it is supplied to the tank.

added other convenient mannerg' dium or potassium chromate to the tank,the Water soluble chromate dissolving in any water present. The chromatemay be added to the tank in crystalline form, in which case it will gointo solution as water is added to or collects in the tank or ifpreferred, a concentrated solution of the chromate in water may be addedto the tank and this will be diluted by any water present in oraccumulating in the gasoline and will thus protect the tank fromcorrosion. If the water is not removed from the gasoline, it will benecessary to prevent it from going to the motor and this may be readilyaccomplished by suitable traps or other devices.

In the so-called aqua system of removing gasoline in storage tanks bypumping water into the tanks and thus forcing th gasoline out at thetop, corrosion of the tank by the combined action of the Water and ametal in the gasoline may be inhibited or prevented by dissolving in thewater a chemical such as a water soluble The chromate may be added tothe In the former chromate.

As previously described, the chromate may be introduced as crystals orin other dry' form or it may be introduced as a concentrated solution inwater. If introduced in dry form, it may be as loose crystals orv placedin a bag or other container or I added. in any However, since any Waterwhich goes into the system, be-

ing heavier than gasoline, .will gravitate to the lower portion of 'thesystem the chromate should be placed at such point, which in most casesis, preferably, the lowest point in the tank. Any water getting into thetank or system will thus settle and dissolve the chromate whereby itwill be made effective. Although the concentration of chromate requiredto eflectively inhibit the corrosion is small, the total amount addedwill obviously depend upon the particular conditions in any given case,such as the size and construction of the tank, the amount of gasoline,the amount and kind of metal compound contained in the gasoline and theamount .of water collecting in the system. Although any ,modificationsmay be made therein without departing from the spirit of the inventionor the scope of the appended claims.

What I claim is:

1. In a gasoline tank or aluminum-containing construction, water inwhich a chromate is dissolved and gasoline which has mixed therewith acompound of a metal which is electropositive to aluminum.

2.,The method of inhibiting the corrosion of aluminum by the combinedaction of water and gasoline containing tetra ethyl lead which com-.prises adding to the water a water-soluble chromate.

3. The method of inhibiting the corrosion, in the presence of moisture,of a tank of aluminumcontaining construction which holds gasoline'containing tetra ethyl lead which comprises placing in the bottom ofthetank a water-soluble chromate.- l

4. The method of inhibiting the corrosion of aluminum in the presence ofWater and gasoline containing an organic derivative of a metalelectropositive to aluminum which comprises adding to the gasoline awater-soluble chromate.-

5. The method of inhibiting the corrosion of aluminum by the combinedaction oi. water and gasoline containing an anti-knock compound which isan organic derivative of a metal electropositive to aluminum whichcomprises adding to the Water a small amount of potassium dichromate. rl. r

6. Inv a tank of aluminum-containing construction, gasoline whichcontains tetra ethyl lead and an aqueous solution of potassiumdichromate. I

- PAUL D. FFIELD.

